Nitrogen dioxide - photolysis

Small differences in light sources have definite effects on photochemical processes. Some irradiation systems match the solar spectrum poorly, thus affecting the relative importance of the various photodissociation processes occurring in the atmosphere. Ambient variations in the nitrogen dioxide photolysis pseudo-first-order rate constant,... 

Nitrogen dioxide photolysis is a key driver of tropospheric atmospheric chemistry since it leads directly to the production and eventual consumption of ozone during the daytime as follows ... 

Schuck, E.A., E.R. Stephens, and R.R. Schrock (1966), Rate constant ratios during nitrogen dioxide photolysis, J. Air Poll Control Assoc., 16, 695-696. 

Laser-induced electronic fluorescence. Two devices reported recently look very promising for continuous atmospheric monitoring. Sensitivities of 0.6 ppb for nitrogen dioxide and ppb for formaldehyde are claimed. Careful attention to possible interference from other species is necessary. Detection of the hydroxyl radical in air ( 10 molecules/cm ) has been claimed for this technique, but it has been pointed out that this concentration seems much too high, especially because the air had been removed fix>m the sunlight 6 s before analysis spurious effects, such as photolysis of the ozone in the air by the laser beam and two-photon absorption by water vapor, might have been responsible for the hydroxyl radical that was observed. 

Photolytic. Photolysis of acetone in air yields carbon monoxide and free radicals, but in isopropanol, pinacol is formed (Calvert and Pitts, 1966). Photolysis of acetone vapor with nitrogen dioxide via a mercury lamp gave peroxyacetyl nitrate as the major product with smaller quantities of methyl nitrate (Warneck and Zerbach, 1992). 

In a solution containing oxygen, photolysis yields a mixture of 6,12-, 1,6-, and 3,6-diones. Nitration by nitrogen dioxide forms 6-nitro-, 1-nitro-, and 3-nitrobenzo[a]pyrene. When benzo [a] pyrene in methanol (1 g/L) was irradiated at 254 nm in a quartz flask for 1 h, the solution turned pale yellow. After 2 h, the solution turned yellow and back to clear after 4 h of irradiation. After 4 h, 99.67% of benzo[a]pyrene was converted to polar compounds. One of these compounds was identified as a methoxylated benzo[a]pyrene (Lu et al, 1977). A carbon dioxide yield of 26.5% was achieved when benzo [a] pyrene adsorbed on silica gel was irradiated with light (A, >290 nm) for 17 h (Freitag et al, 1985). 

Irradiation of gaseous formaldehyde containing an excess of nitrogen dioxide over chlorine yielded ozone, carbon monoxide, nitrogen pentoxide, nitryl chloride, nitric and hydrochloric acids. Peroxynitric acid was the major photolysis product when chlorine concentration exceeded the nitrogen dioxide concentration (Hanst and Gay, 1977). Formaldehyde also reacts with NO3 in the atmosphere at a rate of 3.2 x 10 cmVmolecule-sec (Atkinson and Lloyd, 1984). 

Tuazon et al. (1984a) investigated the atmospheric reactions of TV-nitrosodimethylamine and dimethylnitramine in an environmental chamber utilizing in situ long-path Fourier transform infared spectroscopy. They irradiated an ozone-rich atmosphere containing A-nitrosodimethyl-amine. Photolysis products identified include dimethylnitramine, nitromethane, formaldehyde, carbon monoxide, nitrogen dioxide, nitrogen pentoxide, and nitric acid. The rate constants for the reaction of fV-nitrosodimethylamine with OH radicals and ozone relative to methyl ether were 3.0 X 10 and <1 x 10 ° cmVmolecule-sec, respectively. The estimated atmospheric half-life of A-nitrosodimethylamine in the troposphere is approximately 5 min. 

Oh, D., W. Sisk, A. Young, and H. Johnston, Nitrogen Dioxide Fluorescence from N205 Photolysis, J. Chem. Phys., 85, 7146-7158 (1986). 

The fates of the G(-H) radicals in DNA are mostly determined by reactions with other substrates. Here, we consider the reactions of the G(-H) radicals with types of free radicals that are generated in vivo under conditions of oxidative stress. One of these radicals is the nitrogen dioxide radical, NO2. This radical can be generated in vivo by the oxidation of nitrite, N02, a process that can be mediated by myeloperoxidase [111, 112] as well as by other cellular oxidants [113, 114]. An alternative pathway of the generation of NO2 is the homolysis of peroxynitrite [102, 115] or nitrosoperoxycarbonate formed by the reaction of peroxynitrite with carbon dioxide [99-101]. The redox potential, E°( NO2/NO2")=1.04 V vs NHE [116] is less than that of guanine, E7[G(-H)7G] = 1.29 V vs NHE [8]. Pulse radiolysis [117] and laser flash photolysis [109] experiments have shown that, in agreement with these redox potentials, N02 radicals do not react with intact DNA. However, N02 radicals can oxidize 8-oxo-dG that has a lower redox potential ( 7=0.74 vs NHE [56]) than any of the normal nucleobases [109]. 

The reactions of reactive ground state atomic triplets with organic compounds have been studied most extensively with oxygen atoms. Direct photolysis of oxygen or nitrogen dioxide yields O P) atoms, but Cvetanovic s method of photosensitizing the decomposition of N20 with excited mercury triplets9 in the presence of various pressures of... 

This gives a value of 1.0 sec-1 at 298°K. Ford149 reported a value of 0.44 sec-1 for the same combination of rate constants at room temperature as deduced from the photolysis of nitrogen dioxide in large excesses of oxygen with trace quantities of ozone present. 

Husain and Norrish215 obtained a measurement of k5 in the isothermal flash photolysis of nitrogen dioxide at room temperature. Their calculations depend on knowing the concentrations of N02, N03, NO, and O obtained by calibration of photographic plates and material balance and on knowing the value of the rate constant for the reaction... 

The photochemical processes of triatomic molecules have been extensively studied in recent years, particularly those of water, carbon dioxide, nitrous oxide, nitrogen dioxide, ozone, and sulfur dioxide, as they are important minor constituents of the earth s atmosphere. (Probably more than 200 papers on ozone photolysis alone have been published in the last decade.) Carbon dioxide is the major component of the Mars and Venus atmospheres. The primary photofragments produced and their subsequent reactions are well understood for the above-mentioned six triatomic molecules as the photodissociation involves only two bonds to be ruptured and two fragments formed in various electronic states. The photochemical processes of these six molecules are discussed in detail in the following sections. They illustrate how the knowledge of primary products and their subsequent reactions have aided in interpreting the results obtained by the traditional end product analysis and quantum yield measurements. 

Nitrogen dioxide is about 20 to 50% of the total nitrogen oxides NO, (NO, NOz, HN03, N2Os), while CIO represents about 10 to 15% of the total chlorine species CIO, (Cl, CIO, HCI) at 25 to 30 km. Hence, the rate of ozone removal by CIO, is about equal to that by NO, if the amounts of NO, are equal to those of CIO,. According to a calculation by Turco and Whitten (981), the reduction of ozone in the stratosphere in the year 2022 with a continuous use of chlorofluoromethanes at present levels would be 7%. Rowland and Molina (843) conclude that the ozone depletion level at present is about 1%, but it would increase up to 15 to 20% ifthechlorofluoromethane injection were to continue indefinitely at the present rates. Even if release of chlorofluorocarbons were stopped after a large reduction of ozone were found, it would take 100 or more years for full recovery, since diffusion of chlorofluorocarbons to the stratosphere from the troposphere is a slow process. The only loss mechanism of chlorofluorocarbons is the photolysis in the stratosphere, production of HCI, diffusion back to the troposphere, and rainout. 

Molecular oxygen photodissociation is feeding reaction (1) with atomic oxygen in the stratosphere, the part of the atmosphere extending from above the troposphere to about 50 km. In the troposphere, the lowest part of the atmosphere extended up to 7-16 km, 02 photolysis is not significant. Nitrogen dioxide (N02) photolysis provides the required 03P for 03 production ... 

Photolysis of nitrogen dioxide as a source of oxygen atoms has been employed by Sato and Cvetanovic (87-90) to study their reactions with several olefins. They found a long-wavelength threshold for the oxidation of 1-butene by N02 at around 4047 A. The reaction occurred at this wavelength but not on irradiation with the very intense line at 4358 A. In the same spectral region Dickinson and Baxter (34) and Norrish (78) had found previously a threshold for the photochemical decomposi-... 

A very important question is of course whether in the photolysis of nitrogen dioxide free oxygen atoms are indeed formed or the observed reactions are due to long-lived excited N02 molecules. At around 3700 A. predissociation has been observed and there is little doubt that in the spectral region 3700 to 2450 A. decomposition into NO and ground-state... 

The nitrating agent nitrogen dioxide can be produced in surface waters by nitrate photolysis (Equation 17.16) and nitrite oxidation (Equation 17.19). It is unstable in aqueous solution and can either undergo dimerization and hydrolysis (Equations 17.44 and 17.45), or react with dissolved organic compounds ... 

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